Cathode bat oscilloscope



Aug. 4, 1942. s. BAGNO Erm.

` cATHoDE- Ru oscxLLoscorE .original Fild Jan. 17, 1955 v lNvENToR JInToRNEYVA Reiuued Aug. 4, 1942 N. Y., assignors to Radio Corporation of America, New York, N. Y., a corporation of Dela- Original No. 2,151,313, dated March 21, 1939, Se-y rial No. 2,310, January 17, 1935. Application 1 for reissue March 19, 1941, Serial No. 384,9

29 Claims. (Cl. 5l-,183)

This invention relates to frequency modulation circuits, more particularly to method and means for obtaining the frequency response curve of a circuit, and more especially to a new and improved method of cathode ray-oscilloscopy.

One object of the invention isto provide a cathode ray oscilloscope which by its combination of sub-circuits permits rapid and accurate determination of the wave-form distortion characteristics of various apparatus used in the communications art. Y

Another object of the invention is to provide a cathode 'ray oscilloscope which will enable rapid and proper adjustment or augment of intermediate and radio frequency amplifiers and other parts during the manufacture of such apparatus or in their subsequent servicing.

. Another object of the invention is to provide av cathode ray oscilloscope which will combine all the elements necessary for its operation in one compact unit.

Another object of the invention is to provide a cathode ray oscilloscope of such wide frequency range and versatility as to permit its use as a general test instrument. Another object is to maintain' the test fre- A quency band at constant width despite changes in the location of the band in the complete frequency spectrum.

Another object is to stabilize the frequency modulated oscillator of the apparatus against changes in tube parameters, and over the entire frequency band.

Another object is to eliminate mechanically moving parts, such as electric motors or the like, and to instead make the equipment wholly electrical, inexpensive, and dependable.

Another object is to make the apparatus operable in direct respo to ordinary A C. power lines; to use the power line A. C. as a constant frequency source for modulation: and to use a modulation wave not only for modulation, but also for sweep and for "occulting", whereby all of the operations are kept in perfect synchronism.

Another object is to so relate the modulating S11, S12, S13, S14, S15, Sm. The primary P11 is connected to the standard voltage (usually 115) alstream emitted by the cathode of said tube on the way to the anode is both accelerated by the intermediate positive potential and concentrated into a ilne beam.

' The combination of the secondary S11 and rectiiler valve T: (type 84" say) establish a potential across the condenserCm, and permit a current wave and the sweep wave that the frequency response curve plotted by the apparatus may be read' correctly on a single scale, without distortion, despite changes in power line voltage.

Other objects and, advantages will appear from the ensuing description taken in conjunction with the accompanying drawing.

Referring to the drawing, a power transformer .is provided having a primary P11 and secondaries 55 proportional to said voltage to flow thru the primary Pz1 and resistor Ru. The potential across Rza will then be proportional to the current flowing thru P21. By making the resistance of Ras sumciently high, and introducing the blocking condenser Cn, the A. C. component across Rza is picked up without phase alteration and fed to the horizontal plates of the cathode ray` tube Ts, effecting a linear sweep.

In other words, condenser Cza with associated load resistor Ran function to generate a modulating wave, preferably an approximate saw tooth wave, in this case at the power line frequency, say cycles. vThis saw tooth wave is applied to the horizontal deectors of the cathode ray tube To, to produce sweep, or more broadly, physical motion in a horizontal direction. As will (600 kilocycles say) and radio-frequency buffer' stage. With the current flowing thru the primary Pn of suiiiciently high value, the saturation characteristics of the iron core are periodically varied. The tuned section ofthe oscillator thus alters in stipulated amount and assumes frequency modulated characteristics.

In other words the oscillator 'It is a frequency Vall-wave oscillator and frequency mixer.

Saz, and passed on in desired amount via the voltq age divider Rn and potentiometer Rin.

In other words, frequency modulated output oi' oscillator T: is controlled or attenuated to the desired amount, this being done in the present case by a suitable attenuator indicated at Re, Riu. This control or attenuationpreferably takes place as shown, that is, ahead of the generation of the final test signal, that is, ahead of oscillator T4.

The value T4, (type SAT say) in combination with the tuned coupling inductances G and condensers C1o-C11-Cn-C14-C1s and I resistors R11- .Riza-xs---Ft1-R15---R1c--IR.1'1, serves as an Thus the combination of the circuits built around Ts and T4 provide a carrier frequency of one desired value modulated by a second frequency periconverted to any desired different mean frequency by heterodyning the frequency modulated wave with a carrier wave generated in oscillator T4. Oscillator Ta is essentially a fixed tuned oscillator arranged for frequency modulation. Oscillator T4 is essentially a variably tuned oscillator arranged for amplitude modulation. By mixing the two waves in T4. which functions as detector as well as amplifier. the variable frequency band may be shifted to a different point in the complete spectrum. 'I'he advantages of using two oscillators in this manner, instead of directly changing the tuning of the first oscillator, are that with our system, a tremendous range is available, the shift being either upward or downward, and the shift in mean frequency is obtainedwithout accompanying change of band width.

At the terminals D will be found the carrier and its sidebands. Attenuation of these latter to the desired value is accomplished by the modulator grid potentiometer Rio and voltage divider Re. To these terminals are connected the input of the apparatus under test. The output of such apparatus under radio-frequency test is fed into terminals I-2 if it has its own rectier; other- Wise into 2 4 with I-3 shorted. The valve T5, (type 75 say), serves as a-` diode rectifier and words, the tuning or reaetance of the parallel and cathode ray tube Te connected to the secondary S24.

In other words, the cathode ray is occulted during the quick or return sweep. The preferably saw tooth modulating wave is itself used to occult the ray. Secondary coil S24 develops the desired negativeor occulting potential during the return sweep, and then the rate of change of the modulated oscillator is attained by the series-resonance circuit comprising the lower half of S.: and condenser Ca: and with this circuit, variations in plate impedance have substantially no eilect on the phase angle of the voltage fed to the grid of Ta.

It will be understood that because the inductance of the lower coil of Sz: is varied at the same time as the inductance of the upper coil. the sta- `bilization of the oscillator is maintained over the entire frequency modulation range. In other series resonant circuits being varied together, the series circuitis held at zero reactance throughout the range of the frequency modulation.

The secondary Sie is used to provide filament current for the valves Ts-Ti-Ts.

Numerous modifications will readily suggest themselves to ,those skilled in the art without departing from the spirit and scope of this invention. We are for instance aware that the coupling between band modulator and carrier frequency generator need not be inductive; that resistance coupling need not be employed for the output of T5; that the filter circuits shown may assume a variety of forms; and that the adjustments auxiliary to the indicator M may be coaudio amplifier; and the output of same is made to control the vertical sweep of the electron beam in the cathode ray tube Ts.

It will be understood that because of the limited range of responsiveness of the circuit undergoing test, only one band of the energy at D is effective or need be usedfor test, the carrier and other bands departing too far to be effective. The frequency of oscillator .T4 of course, selected or adjusted with this in mind.

Due to hysteresis effects resulting from the periodically varying saturating currents supplied to P21, or wherever the modulator frequency wave form is assymetric, the curves traced out by the cathode ray tube in the forward and reverse sweeps of the electron beam will diier. This undesirable condition `is avoided by blocking out one of the traces via an additional grid in the ordinated and made automatic; and that the exact nature and number of the electron valves shown may be varied.

Also that various means may be used to generate the modulating wave; that the modulating wave need not be an approximately saw tooth wave; that various means may be used to frequency modulate the oscillator T3; that various means may be used to modulate the output of oscillator T4 with the output of oscillator T3; that it is not essential to use two oscillators, especially for limited test range; that the amplifier rectifier tube Ts is not essential, though desirable; that various means to occult the cathode ray may be used: and that occultation is not essential, though desirable.

In the specification and 'in the appended claims, the term "frequency response curve refers broadly to any frequency response characteristic which may be fiat or peaked, as well as curved. The terms circuit to be tested" or test circuitr include an electrical element or a distributed line, as well as a conventional resonance circuit, or in other words, we refer to anythingY which itmay be desirable to test for frequency response.

Having now set forth` the object and nature of our invention, and described instrumentalities embodying the principles thereof, and illustrated the method pertaining thereto, what we claim as new and useful and of our own invention and dosire tosecure by Letters Patent is:

1. Apparatus devoid of motor-driven ork like mechanically moving mechanism for obtaining the frequency response of a circuit, said appa- .ratus comprisingan oscillatorincluding a tuned circuit, a source of modulating. curi-ent, mechanically static frequency modulation means for said oscillator arranged to be coupled to said source, means for applying the resulting frecore, a coil for applying the aforesaid saw-tooth wave to the iron core in order to vary the saturation thereof so as to vary the frequency of the oscillator, means for applying the frequency modulated energy to the circuit to be tested, means responsive to the output of the test circuit to produce physical motion in one direction, and means responsive to the saw-tooth wave to produce physical motion in a different coordinate direction in orderto plot the desired frequency response characteristic.

3. Apparatus for obtaining the frequency response of a circuit, said apparatus comprising a power transformer for connection to an altemating current power line, a rectifier connected thereto, a condenser and associated load resistor connected to said rectifier for producing an approximate saw-tooth wave, an oscillator coupled to an iron core, a coil for applying the aforesaid saw-too'th wave to the iron core in order to vary the saturation thereof, means for. applying the resulting modulated energy to the circuit to be tested, and means responsive to the output of the test circuit to produce physical motion in one di- .rection and means responsive to the saw-tooth wave to produce physical motion in a different l5. An apparatus for vdetermining frequency phenomena in an electric 'circuit to be tested, comprising means for generating a first frequency wave, means for generating a second frequency wave, means for frequency modulating said second frequency wave by said first frequency wave, means for -generating a third frequency wave, means for amplitude modulating said third frequency wave by said frequency modulated y wave, output terminal means adapted to feed the wave resulting from said successive modulations into an electric circuit to be tested, input terminal lmeans 'adapted to receive.c urrent from a circuit to be tested, and means connected across said input terminal means for determining the.

frequency characteristics of said circuit.

6. An apparatus for continuous visual projection of thefrequency response of a circuit, said apparatus comprising means for generating a first frequency wave, means for generating a second frequency wave, means for frequency modulation of said second by said rst frequency wave, a variably tunable oscillator for generating a third frequency wave, means for amplitude modulating said third frequency wave by said frequency modulated' wave, means for predeto receive current from a circuit to be tested, and

means including a`n oscilloscope connected across said input terminal means for visualizing the frequency characteristics of said circuit.

7. An apparatus for obtaining frequency'modulated Waves for visualization, comprising means for generating a substantially constant frequency rst alternating. current of predetermined frequency, means for generating a second alternatcoordinate direction, in order to plot the desired frequency response characteristic.

4. Apparatus for obtaining the frequency response of' a circuit, said apparatus comprising means arranged for connection to an alternating current power line for producing an approximate saw-tooth wave, an oscillator including a tuned input circuit 'and an output circuit having an inductance and condenser in series and resonant to the frequency of the input circuit in order to stabilize the oscillator, said inductance being coupled to the inductance of the input circuit and both being coupled to an iron core, a coil for applying the aforesaid saw-tooth wave to the iron core in order to vary the saturation thereof so as to vary the frequency of the oscillator, means tion in a different coordinate direction in order (lll ing current of predetermined frequency, meansl for frequency modulating said second current substantially in accordance with the wave form and amplitude of said first current, and a cath` ode ray tube having two deiiecting means to deflect an electrical beam in two different planes, one of said deilecting means being `connected in circuit with said iirst alternating current and being responsive to electrical changes in said first alternating current.` e

A8. Apparatus for obtaining the frequency response of a circuit, said apparatus comprisingv means for producing an approximate saw-tooth wave, an oscillator, frequency modulation means for applying the aforesaid saw-tooth wave to the oscillatorln order to vary the frequency of the oscillator, means for applying the modulated energy to the circuit to be tested, a cathode ray tube having deflection means, means to apply the output of the test circuit to the vertical deflection means, and means to apply the sawtooth wave to the horizontal deflection means. y

9. Apparatus for obtaining the frequency re sponse of a circuit, said apparatus comprising a source of a modulating wave, an oscillator in- 'cluding a tuned circuit having an inductance `coupled to an iron core, a coil forapplying the aforesaid modulating wave to the ironl core in order to vary the saturation thereof so as to vary the .in Plot the desired frequency response charac- `teristic.

frequency of the oscillator, means for applying the frequency modulated energy to the circuit to be tested, a cathode ray tube and deflection i erating a second alternating current of predemeans therefor, means to apply the output of the test circuit to the vertical deflection means, and means to apply the modulating wave to the horizontal deflection means.

10. Apparatus for obtaining the frequency re.-

sponse of a circuit, said apparatus comprising means for producing a modulating wave, an oscillator, means responsive to the aforesaid modulating wave to'vary the frequency of the oscillator, means for applying the frequency modulated energy to the circuit to be tested, a cathode ray tube and deflection means therefor, means to apply the output of the test circuit to the vertical deilection means, means to apply the modulating wave to the horizontal deflection means,

i output of the test vcircuit to the amplifier tube,

optionally useable means to provide rectification in said amplifier tube, a cathode ray tube and deflection means therefor, means to apply the outputof the amplifier to the `vertical deflection means, and means to apply the saw-tooth wave to the horizontal deflection means.

12, Apparatus for obtaining the frequency response of a circuit, said apparatus comprising means for producing a modulating wave', a first f oscillator, frequency modulating means responsiv'e to said modulating wave for varying the frequency of the oscillator, a second oscillator,

` means to vary thefrequency thereof, means to amplitude modulate the second oscillator in accordance with the frequency modulated output of the first oscillator, means for applying the resultant modulated energy to the circuit to be tested, a cathode ray tube and deflection means therefor, means to apply the output of the test circuit to the vertical deflection means, means to` apply the modulating wave to the horizontal deflection means, and means responsive to the modulating wave to occult the cathode ray during its return sweep.

13.1Apparatus for obtaining the frequency response curve of a circuit, said apparatus comprising a source of modulating wave, an oscillator including a tuned circuit having an inductance coupled to an iron core, a coil for applying the aforesaid modulating wave to theviron core in order to vary the saturation thereof so as t vary the frequency of the oscillator, means for applying the modulated energy to the circuit to be tested, a cathode ray tube and deflection rneans-therefor, means to apply the output of the test circuit to the vertical deflection means, means to apply the modulating wave to the horitermined frequency, frequency modulating said second current substantially in accordance with the wave form vand amplitude of the first current, generating a stream of electrons, and d eiiecting said stream in' two different directions in synchronism with variations in said first alternating current.

15. In a method for obtaining a frequency response curve of a circuit for visualization, the steps of generating a first alternating current of substantially constant predetermined frequency, generating a second alternating current of predetermined frequency, frequency modulating said second current by said rst, generating a third alternating current of predetermined frequency, amplitude modulating'said third current by the alternating current resulting from said frequency modulation of said second current by said first, vfeeding the resulting current to the circuit to be tested, transforming electrical variations of said resultant output current of said test circuit into physical motion in one direction, and at the same time transforming the first alternating current into physical motion in a different coordinate direction in order to plot the desired frequency response curve.

16. In the testing of wave-responsiveapparatus, the method which includes first generating a frequency modulated wave at any desired part of the frequency spectrum, the band or frequencyA range of variation of which is substantially constant over all parts of the frequency spectrum, by the steps of frequency modulating a constant frequency carrier, thereafter amplitude modul lating another constant frequency carrier by means of the frequency modulated carrier, determining the location in the frequency'spectrum of the variable frequency band by adjustment of the ycircuit characteristics of the circuit modulating a constant frequency carrier, attenuating the frequency modulated carrier to dezontal deflection means, and means to occult the sired value, thereafter amplitude modulating another constant frequency carrier bymeans of the attenuated frequency modulated carrier, and causing the apparatus to be tested to respond to one of the side bands of the last-named `modulation.

18. In a method for obtaining a .frequency modulated wave for visualization of the frequency response of a circuit to be analyzed, the steps of generating a first alternating current of substantially constant predetermined frequency, generating a second alternating current of predetermined frequency, frequency modu-- lating said second current by said first, generating a third alternating current of predetermined frequency, amplitude modulating said third current by the alternating current resulting from said frequency modulation of said second current by said first, feeding a side band of the resulting modulated wave to the circuit to be analyzed, generating a stream of electrons, and

deflecting said stream by components in two directions, one component being obtained in response to the output of the circuit to be analysed, and the other component being obtained in response to the aforesaid first frequency wave.

19. An apparatus devoid of motor-driven or like mechanically moving mechanism for continuous visual projection of the frequency response curve of a circuit to be tested comprising means for generating w'ave energy of a first frequency, means for generating wave energy of a second frequency, mechanically-static frequency modulating means for modulating the energy of the second frequency by the energy of the first frequency, a variably minable oscillator for generating wave energy of a third predetermined frequency, means for amplitude-modulating said third frequency energy by said frequencymodulated energy, output terminal means adapted to feed the wave energy resulting from said successive modulations into the circuit to be tested, in-

put terminal means adapted to' receive current from the circuit to be tested, and means including anr oscilloscope connected across said -input terminal means for visualizing the frequency characteristic of said circuit.

20. Apparatus devoid of mechanically driven mechanism for continuous visual projection of a frequency response curve of a circuit to be tested, said apparatus comprising meansresponsive to an alternating current power supply source for producing energy whose time variation is of substantially triangular wave shape and constant frequency and in direct timed relation therewith, an oscillator, mechanically-static frequency modulation means for modulating the frequency of the oscillator under the control of said energy, means for applying frequency-modulated energy from said oscillator to the circuit to be tested, a cathode ray tube having beam forming means and a target, two mutually perpendicular deection means for controlling the position of impact of the beam on the target, means to apply energy representative of output energy of the test circuit to one of the deection means, and means to apply triangular wave shape energy to the other of lthe deflecting means, the frequencyof said triangularwave shape energy having a factor common with the frequency of the alternating current power supply whereby a stationary image is produced on the target of the cathode n ray tube.

2l. Apparatus devoid of mechanically driven mechanism for continuous visual projection of a frequency response curve of a circuit to be tested, said apparatus comprising means responsive to an alternating current power supply source for producing energy whose time variation is of substantially triangular wave shape and in direct timed relation therewith, an oscillator, mechanically-static frequency-modulation means for modulating the frequency of the oscillator under the control of said energy,means for applying frequency modulated energy from said oscillator to the circuit to be tested, a cathode ray tube having beam forming means and a target, two mutually perpendicular deflection means for controlling the position of impact of the beam on the target, an amplifier tube, means to supply output energy of the test circuit to said amplifier tube,

22. Apparatus devoid of mechanically driven mechanism for continuous visual projection of a frequency response curve of a circuit to be tested. said apparatus comprising means responsive to an alternating current power supply source -for producing energy whose time variation is ofv subl.

stantially triangular wave shape and in direct timed relation therewith. a first oscillator, mechanically-static frequency-modulation means for modulating the frequency of the oscillator under the control of said energy, a 4second oscillator, means to amplitude-modulate energy of the second yoscillator in accordance with said frequency-modulated energy, means for applying the modulated energy from said second oscillator to the circuitto be tested, a cathode ray tibe having beam forming means and a target, two mutually perpendicular deflection means for controlling the position of impact of the beam on the target, means to apply energy representative of output energy of the test circuit to one of the deflection means, means to apply triangular wave shape energy to the other of the defiecting means, the frequency of said triangular wave shape energy having a factor common with the frequency of the alternating current power supply, whereby a stationary image is produced on the target of the cathode ray tube and control means to adjust the frequency of said second oscillator to a predetermined frequency. Y

23. An apparatus devoid of mechanically driven mechanism for continuously projecting the frequency responsemof a circuit to be tested for visualization, said apparatus comprising means responsive to an'alternating current power supply for generating a substantially constant frequency current of triangular wave shape and in timed relation to the alternating current power supply, means for generating an`alternating current of higher frequency than said con-4 stant frequency, means for frequency modulating said higher frequency current substantially in` accordance with the fwave form and amplitude of said constant frequency current, means to supply the frequency modulated current to the circuit to be tested, and a cathode rayl tube having a screen and two deecting means to deect an electrical beam in two different planes, one of said deilecting means being energized in timed relation to the alternating' power supply,` andv the other deilectlng 'means being responsive to the frequency modulated current from the circuit being tested, whereby the two deflecting v driven mechanism for continuously projecting optionally usable means to provide rectification the frequency response of a circuit to be tested for visualization, said apparatus comprising an alternating current power supply, means for generating energy whose time variation is of substantially triangular wave form of a predetermined frequency and in timed relation to 'the alternating current power supply, a local oscillator for generating an alternating current of higher frequency than said Ipredetermined frequency, l means for frequency modulating said higher frequency current substantially in accordthe frequency response c tested for visualization free from mechanically ance with the wave form and amplitude of energy from the triangular wave generating means, means to supply the frequency-modulated current to the circuit to be tested, and a cathode rayv tube having a target to receive a beam of electrons and two deflectng means to deect said electron beam in two diiferent planes, means to 4 energize 'one of said deecting means in response to energy from the triangular wave generating apparatus, and means to energize the other of the detlecting means in accordance with the frequency-modulated current from the circuit being tested, whereby the two deilecting means are er1- ergized in timed relation to the alternating cur' rent power supply to produce a stationary image on the target of the cathode ray tube.

25. Inla method for continuously projecting the frequency response curve of a' circuit to be f tested for visualization free from motor-driven or like mechanically moving mechanism, the steps of generating energy whose time variation is of substantially triangular wave shape from an alternating current power supply and in timed relation therewith, generating an alternating current of higher frequency than that of said energy, frequency-modulating said higher frequency y current substantially in accordance with the waveform and amplitude of the triangular wave shape energy, applying the frequency modulated ergy whose time variation is of substantially triangular wave form from an alternating current power supply and in timed relation therewith, generating an alternating current of higher fre- 'quency than said energy, frequency-modulating stream on a target area, deflecting said stream' l image on the target area.

current to the circuit to be testedgenerating a stream of electrons in a cathode ray tube having a target impacted by the generated stream, 'and deflecting said stream in two different directions, 'j

the deflection in one direction being in timed relation with the alternating current power supply and the deflection in the other direction being in response to the circuit being tested, whereby a stationary response curve is produced on the target.

y26. In a method for continuously projectixg the frequency response curve of a circuit to be tested for visualization free from mechanically moving mechanism, the steps of generating en- Y rection in response to energy of triangular wave form, defiecting said stream in another direction in response to frequency-modulated current from the circuit being tested,` and producing a stationary visible trace by the doubly deflected stream of electrons.

27. In a method for continuously projecting e of a circuit to be moving mechanism, thesteps of generating envon one coordinate axis in response to triangular wave Ienergy, deecting'said stream on an axis transverse to said coordinate axis in response to frequency-modulated current from the circuit being tested, the sweep time in one direction and the modulation swing in one direction both corresponding to the time interval oi' change of the -triangular wave energy in one direction, whereby thedeflection on both axes produces a stationary 28. Apparatus. for continuous visual projection of the frequency response of a circuit, said appa'- ratus comprising a power transformer for connection tol an alternating current power line, a rectifier, a condenser and associated load resistor connected to said rectifier for producing energy whose time variation is of substantially triangular wave shape, an oscillator, means for applying the aforesaid energy to vary the frequency of the oscillator by modulation, means to 'apply modulated energy from the oscillator to a circuit to be tested, a cathode ray tube having vertical and horizontal deflection means, means to apply the output of the test circuit to the vertical defiection means, and means to apply the first named energy to the horizontal deflection ulation means for applying the aforesaid energy to the oscillator in order to vary the frequency of the oscillator, a second oscillator, means to amplitude modulate the second oscillator in accordance with the frequency modulatedr output of the rst oscillator, means for applying the resultant modulated energy to a circuit to be tested, adjustable means to vary the frequency of the second oscillator in order to determine the approximate test frequency applied to the circuit, a. cathode ray tube having vertical and horizontal deflection means therefor, means to apply the output energy of the test circuit to the vertical deection means, and means to apply the first named energy to the horizontal deflection means.

SAMUEL BAGNO. MARI'JN POSNER. 

